New Observations on the Choreotrich Ciliate Strombidinopsis acuminata Fauré-Fremiet 1924, and Comparison with Strombidinopsis jeokjo Jeong et al., 2004

ABSTRACT. A choreotrich ciliate collected in waters off Geoje Island, on the eastern coast of the South Sea of the southern coastal water of Korea was morphologically and biometrically investigated through observations of permanent preparations after protargol impregnations. Morphological data and ciliary patterns indicated that the ciliate should be identified as Strombidinopsis acuminata based on the number of somatic kineties. The vertical distribution of the population abundance was also examined in relation to environmental conditions: higher abundances occurred in surface water with higher temperature (22–23 °C), lower salinity (32 psu), and higher concentration (ca 10 μg/L) of chlorophyll a . The 18S rRNA gene of specimens from clonal cultures isolated from natural assemblages was sequenced. While this isolate of S. acuminata is closer to Strombidinopsis jeokjo (99.6–99.8%) than other isolates of S. acuminata (<99.0%), monophyly of S. acuminata was not rejected by the AU test. We discuss the discordance between morphological and molecular data for Strombidinopsis . In order to confirm the species level of the Strombidinopsis specimens, additional information is required based on genealogical analyses of multiple loci.